Srini's Point of View

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Python development setup on Mountain Lion - part 2

Setup virtualenv and virtualenvwrapper on Mountain Lion

In the previous part I went through how you can have multiple versions of python and how you can easily switch between these versions. Here I will go through setting up virtualenv and virtualenvwrapper. This will help in keeping all the different versions of python pristine!

First step is to switch to whatever version of python you want to do this in. Use the bash switch function we created in part 1.

Next we will install the python package installer pip using the easy_install command.

$ sudo easy_install pip

*Update Start (July-02-2013) *
The above step is not correct. On my mac, I assumed easy_install to be part of the python version I switched to, as described earlier. When I checked the location for easy_install, I realized that it was from the python version shipped with mountain lion. easy_install is part of setuptools. So we will need to install setuptools for the version of python you are using. As I am trying to switch to version 2.7.3, I did the following to install this -

$ curl -o setuptools-0.6c11-py2.7.egg  
$ sudo sh setuptools-0.6c11-py2.7.egg  
$ rm setuptools-0.6c11-py2.7.egg

You should now see easy_install in the bin directory of the python version you are trying to do this for. In my case for python 2.7.3 it was in “/Library/Frameworks/Python.framework/Versions/2.7/bin”. As this is already in my path thanks due to the python switching tools I showed you all from the first part in this series, we are good. Now run “sudo easy_install pip” as first directed and it will install pip in the right version of python.
* Update Finish (July-02-2013)*

Next install virtualenv and virtualenvwrapper using the pip command

$ sudo pip install virtualenv  
$ sudo pip install virtualenvwrapper

Now add the following variables in your .bash_profile before activating virtualenvwrapper

export WORKON_HOME=$HOME/.virtualenvs  

. /usr/local/bin/

Yes, there is a dot in front of /usr/local/bin/
Next go ahead and create the directory .virtualenvs in your home directory.
Now that all the ground work is done, go ahead and source your .bash_profile file. You should see virtualenvwrapper initialise some files and folders under .virtualenvs. It will also add some more bash functions to make your life easy.

Now lets go ahead and create a virtual environment for our python 2.7.3 environment.

$ mkvirtualenv python273  
Installing setuptools...........  
Complete output from command
/Users/username/.v...python273/bin/python -c "#!python  

" /Library/Python/2.7/...ols-0.6c11-py2.7.egg:  
Traceback (most recent call last):  
File "<string>", line 279, in <module>  
File "<string>", line 207, in main  
File "build/bdist.linux-i686/egg/setuptools/", line 2,
in <module>  
File "build/bdist.linux-i686/egg/setuptools/", line 1, in
line 16, in <module>  
exec(open(os.path.join(distutils_path, '')).read())  
IOError: [Errno 2] No such file or directory:
...Installing setuptools...done.  
Traceback (most recent call last):  
File "/usr/local/bin/virtualenv", line 8, in <module>  
load_entry_point('virtualenv==1.7.2', 'console_scripts',
File "/Library/Python/2.7/site-packages/", line 942, in
File "/Library/Python/2.7/site-packages/", line 1052, in
search_dirs=search_dirs, never_download=never_download)  
File "/Library/Python/2.7/site-packages/", line 598, in
search_dirs=search_dirs, never_download=never_download)  
File "/Library/Python/2.7/site-packages/", line 570, in
File "/Library/Python/2.7/site-packages/", line 1020, in
% (cmd_desc, proc.returncode))  
OSError: Command /Users/username/.v...python273/bin/python -c

" /Library/Python/2.7/...ols-0.6c11-py2.7.egg failed with error code 1

Turns out this error came up because Xcode which was installed from the App Store on my new Mountain Lion install did not come with the command line tools. Go to the preference pane in Xcode, and then go to the downloads section and install the command line tools. Once done, go ahead and try the mkvirtualenv command again.

$ mkvirtualenv python273  
New python executable in python273/bin/python  
Installing setuptools............done.  
Installing pip...............done.  
virtualenvwrapper.user_scripts creating
virtualenvwrapper.user_scripts creating
virtualenvwrapper.user_scripts creating
virtualenvwrapper.user_scripts creating
virtualenvwrapper.user_scripts creating
(python273) $ which python  

Notice how my prompt changed to show me which environment I am in. What mkvirtualenv did was create a copy of python under your .virtualenv directory and made it your default python.

There is a slight problem now. I checked to see the version of python in the virtualenv I just created and found that the version was 2.7.2. This was the version of python which came with the new install of Mountain Lion. After reading the docs on mkvirtualenv I found that mkvirtualenv used the python version which was used to install virtualenv.. but I thought I had switched my version of python to use python 2.7.3.. Grr.. ok.. whatever!! I deleted my newly created virtualenv and recreated a new one again, but this time define the version of python I want to use.

$ rmvirutalenv python 273  
Removing python273...  
$ mkvirtualenv python273 -p
Running virtualenv with interpreter
New python executable in python273/bin/python  
Installing setuptools............done.  
Installing pip...............done.

This confirms my python :)

Update Start (July-02-2013) *
If you followed my latest update from above for confirming the existance of easy_install in the version of python you want and installing if missing, the problem with creating the virutalenv instance with the wrong version of python will not happen.
Update finish (July-02-2013)

Here are some commands you will using -

  • deactivate - command will disable the virtual environment.
  • workon - command by itself will show you a list of virtual environments. To activate a particular environment, run ‘workon env_name’
  • rmvirtualenv - run this command with the name of virtualenv to delete that environment

The best part is that now you don’t need the sudo command to install any new python modules as python is now under your home directory. You are now free to use the pip command to install any module you want.

In the next part I will show you how to setup eclipse to use a virtual python environment…